Modern society has quickly adopted, and become reliant upon, handheld devices for wireless communication. For example, cellular telephones continue to proliferate in the global marketplace due to technological improvements in both the communication quality and device functionality. These wireless communication devices have become common for both personal and business use, allowing users to transmit and receive voice, text and graphical data from a multitude of geographic locations. The communication networks utilized by these devices span different frequencies and cover different transmission distances, each having strengths desirable for various applications.
Cellular networks facilitate wireless communication over large geographic areas. These network technologies have commonly been divided by generations, starting in the late 1970s to early 1980s with first generation (1G) analog cellular telephones that provided baseline voice communication, to modern digital cellular telephones. Global System for Mobile Communications (GSM) is an example of a widely employed 2G digital cellular network communicating in the 900 MHz/1.8 GHz bands in Europe and at 850 MHz and 1.9 GHz in the United States. This network provides voice communication and also supports the transmission of textual data via the Short Messaging Service (SMS). SMS allows a wireless communications device (WCD) to transmit and receive text messages of up to 160 characters, while providing data transfer to packet networks, Integrated Services Digital Network (ISDN) and Plain Old Telephone Service (POTS) users at 9.6 Kbps. The Multimedia Messaging Service (MMS), an enhanced messaging system allowing for the transmission of sound, graphics and video files in addition to simple text, has also become available in certain devices. Soon, emerging technologies such as Digital Video Broadcasting for Handheld Devices (DVB-H) will make streaming digital video, and other similar content, available via direct transmission to a WCD. While long-range communication networks like GSM are a well-accepted means for transmitting and receiving data, due to cost, traffic and legislative concerns, these networks may not be appropriate for all data applications.
Short-range wireless networks provide communication solutions that avoid some of the problems seen in large cellular networks. Bluetooth™ is an example of a short-range wireless technology quickly gaining acceptance in the marketplace. A 1 Mbps Bluetooth™ radio may transmit and receive data at a rate of 720 Kbps within a range of 10 meters, and may transmit up to 100 meters with additional power boosting. Enhanced Data Rate (EDR) technology, which is also available, may enable maximum asymmetric data rates of 1448 Kbps for a 2 Mbps connection and 2178 Kbps for a 3 Mbps connection. In addition to Bluetooth™, other popular short-range wireless networks include for example IEEE 802.11 Wireless LAN, Wireless Universal Serial Bus (WUSB), Ultra Wideband (UWB), ZigBee (IEEE 802.15.4 and IEEE 802.15.4a), wherein each of these exemplary wireless mediums have features and advantages that make them appropriate for various applications
The IEEE 802.11 Wireless LAN Standards describe two major components, a wireless device, called a station (STA), and a fixed access point (AP) wireless device. The AP may perform the wireless-to-wired bridging from STAs to a wired network. The basic network is the basic service set (BSS), which is a group of wireless devices that communicate with each other. An infrastructure BSS is a network that has an AP as an essential node.
The access point (AP) in legacy IEEE 802.11 Wireless LAN networks must relay all communication between the wireless devices (STAs) in an infrastructure BSS. If a STA in an infrastructure BSS wishes to communicate a frame of data to a second STA, the communication must take two hops. First, the originating STA transfers the frame to the AP. Second, the AP transfers the frame to the second STA.
The access point in an infrastructure BSS assists those wireless devices attempting to save power. For example two different power states may be supported by wireless devices. In the awake state the wireless device is able to transmit or receive frames and is fully powered, while in the doze state the wireless device is not able to transmit or receive and consumes very low power. In the active mode wireless device should be in the awake state all the time and the power save mode where the STAs alternates between awake and doze states. There may be further power save modes.
The legacy IEEE 802.11e Wireless LAN standards provides for support of low power operation in handheld and battery operated STAs, called automatic power save delivery (APSD). A STA currently in the power saving mode, will wake up at predetermined times to receive beacons received from the AP to listen to a traffic indication map (TIM). If existence of buffered traffic waiting to be sent to the STA is signaled through the TIM, the STA may remain awake and initiate the data transmission from the AP.
There is unscheduled automatic power save delivery (U-APSD) and scheduled automatic power save delivery (S-APSD) defined. In U-APSD, the access point is always awake and hence a STA in the power save mode can send a trigger frame to the AP when the STA wakes up, to retrieve any queued data at the AP and also transmit any data queued from the STA to the AP. In S-APSD, the AP assigns a schedule to a STA and the STA wakes up at the assigned time to retrieve from the AP any data queued for the STA. An AP can maintain multiple schedules either with the same STA or with different STAs in the infrastructure BSS network. Since the AP is never in sleep mode, an AP will maintain different scheduled periods of transmission with different STAs in the infrastructure BSS network to ensure that the STAs get the maximum power savings.
A next generation IEEE 802.11 WLAN standard is being currently developed as the IEEE 802.11 TGz standard, which includes the feature of tunneled direct link setup (TDLS) with channel switching. This feature enables two wireless devices (STAs) in an infrastructure BSS to directly exchange frames of data over a direct data transfer link, without requiring the access point in the infrastructure BSS to relay the frames. However, the IEEE 802.11 TGz standard currently under development does not provide means for multiple STAs to enter into a power saving sleep mode, since the AP is no longer available to buffer the frames in the direct data transfer link between the STAs.